1. Field of the Invention
The present invention relates to a display device and a method for manufacturing thereof. The display device is of the type having a first electrode, more than one organic layer including an emitting layer, and a second electrode, which are sequentially arranged on a substrate, so that the light generated by the emitting layer radiates through the first or second electrode.
2. Description of the Related Art
Among recent flat panel display devices attracting attention is an organic light-emitting display device that employs an organic luminous element. Being selfluminous, it has a wide viewing area, a low power consumption, and a capability of responding to high-speed video signals for high-definition television.
The organic luminous element mentioned above has a first electrode, more than one organic layer including an emitting layer, and a second electrode, which are sequentially arranged on a substrate. In the case where it is used for a display device of active matrix type, the first electrode is formed on a planarized insulating film that covers TFTs (Thin Film Transistors) on the substrate.
In the meantime, the organic light-emitting display device with the organic luminous elements mentioned above is required to be free of dark spots (pixels emitting no light) which are greatly detrimental to the display quality and manufacturing yield. Dark spots are caused by foreign matter adhering to the first electrode during production. Foreign matter adhering to the first electrode entraps air thereunder when an organic layer is formed thereon. The entrapped air causes dark spots when the finished organic luminous element undergoes degassing. Unfortunately, it is difficult to completely protect the first electrode from foreign matter before it is covered with the organic layer.
Thus, there has been proposed a method for reducing the occurrence of dark spots. This method has the steps of providing a transparent electrode (a first electrode) on a substrate and providing a hole transporting layer, with a hole injection layer interposed between them, and finally heating the substrate at a temperature above the glass transition point and below the melting point of the hole transporting layer, thereby melting the hole transporting layer to cover foreign matter. (See Japanese Patent Laid-open Publication No. 2000-91067.)
There has been proposed another method for reducing dark spots. This method has the steps of providing a first electrode on a substrate, providing a hole transporting layer thereon, and finally heating the substrate at a temperature equal to the glass transition point of the hole transporting layer, thereby improving the properties of the hole transporting layer. (See Japanese Patent No. 3473258.)
According to the above-mentioned patent documents, the organic light-emitting display device is produced by the method which is explained below with reference FIG. 5A. The illustrated organic light-emitting display device has the organic light-emitting element comprising a first electrode 14, an organic layer 18 including an emitting layer 18c, and a second electrode 19, which are sequentially arranged on a substrate 11.
As shown in FIG. 5B, which is an enlarged view of the region A in FIG. 5A, the hole injection layer 18a will not completely cover the first electrode 14 if there exists a particle of foreign matter B adhering thereto. A gap C will remain under the foreign matter B.
The hole injection layer 18a is heated at a temperature equal to or higher than its glass transition point (Tg). The result of heating is shown in FIG. 5C. That is, the hole injection layer 18a flows to cover the foreign matter B, thereby eliminating the gap C thereunder (shown in FIG. 5B).